One application of quantum computing is in the computation of molecular properties that are defined by quantum mechanics. Such quantum computations would have a variety of applications such as in pharmaceutical research and development, biochemistry, and materials science. Conventional computing approaches are suitable for only the simplest quantum chemical computations due to the significant computational resources required. Typical many-body systems of interest generally cannot be evaluated. Quantum chemical computational techniques can require significantly fewer computational resources, and permit computation of the properties of many-body systems.
Current approaches to quantum chemical computations exhibit significant limitations. A standard circuit model uses one and two body Hamiltonian terms. This circuit changes basis and then entangles all of the required qubits, rotates the result, unentangles the qubits, and finally changes back to the original basis. While this conventional approach can produce useful results, very large numbers of gate operations are required, and improved approaches are needed.